1. Field of the Invention
This invention relates generally to compositions and methods of treating liver fibrosis or cirrhosis. Specifically, the invention is directed to compositions and methods for killing liver stellate cells.
2. Description of the Related Art
According to the American Liver Foundation, over 300,000 Americans are hospitalized each year for cirrhosis of the liver. The primary causes of cirrhosis are alcohol abuse and chronic hepatitis C. To date, approximately 3.9 million Americans suffer from Hepatits C. It is also estimated that 18,000 people are in need of liver transplants, which are in woefully short supply. Thus, it is essential to saving lives that new medical treatments for preventing and reversing liver cirrhosis are developed.
Hepatitis C virus (HCV) is a major causative agent of acute and chronic hepatitis, which may lead to liver cirrhosis and hepatocellular carcinoma (Choo, Q. L. et al, 1989; Di Bisceglie, A. M. 1997; Saito I. et al 1990). Natural immune responses are not capable of terminating HCV infection in most patients. Furthermore, neither a vaccine nor any other means of very effective therapy is available to control HCV (McHutchison et al., 1998). Immune evasion and a quasispecies nature are prominent features of HCV (Farci et al., 1992; Weiner et al., 1992; Purcell, 1994). The molecular mechanisms whereby HCV circumvents the immune response, persists, and causes chronic liver disease is not well understood. However, these processes would likely require immune mediated factors, and the interaction of viral proteins with cellular factors (Rehermann and Chisari, 2000).
HCV contains a single positive-stranded RNA as its genome. HCV genome encodes a precursor polypeptide of ˜3,000 amino acids. This precursor polypeptide is cleaved by both host and viral proteases to at least 10 individual proteins: C, E1, E2, p7, NS2, NS3, NS4A, NS4B, NS5A, and NS5B (Clarke, B. 1997). Diverse functional activities of the HCV core protein have already been noted by a number of investigators (Ray and Ray, 2001-FEMS). Our own work and the results from other laboratories suggest that the core protein has multifunctional activities. These include encapsidation of viral RNA, a regulatory effect on cellular and unrelated viral promoters, interactions with a number of cellular proteins, a modulatory role in programmed cell death or apoptosis under certain conditions, involvement in cell growth promotion and immortalization, induction of HCC in transgenic mice, and a possible immunoregulatory role. These intriguing properties suggest that the core protein, in concert with diverse cellular factors, may contribute to pathogenesis during persistent HCV infection.
Hepatic stellate cells (HSC) constitute approximately 15% of the total number of resident liver cells, and are the pivotal cell type involved in the development of hepatic fibrosis (McGee J O, J Pathol; 106, 1972; McGee J O, Lab Invest; 26:429-440, 1972). Following liver injury of any etiology, HSC are activated from quiescent cells into proliferative, fibrogenic, and contractile myofibroblasts (Friedman, 2000, and Proc Natl Acad Sci USA 1985; 82: 8681-8685. and Rockey D C, Submicrosc Cytol Pathol 1992; 24:193-203.). The survival of activated HSC in liver injury is dependent on soluble growth factors and cytokines, and on components of the fibrotic matrix (Iredale, 2001).
Liver fibrosis is a central feature of the majority of chronic liver injuries due to metabolic, genetic, viral, and cholestatic diseases. It results in distortion of the liver architecture (cirrhosis), which is associated with disturbance of liver function and significant morbidity and mortality (Friedman S L. N Engl J. Med., 328:1828-1835, 1993). During the liver injury these cells are activated and the process involves cell proliferation and acquisition of fibrogenic and contractile capacity. Liver hepatocytes plays an important role in this activation (Smith et al; 2003; Hepatology). The resolution of hepatic fibrosis is associated with the remodeling of the excess liver matrix and may result in restitution of near normal liver architecture in patients (J. F. Dufour, et al Dig Dis Sci. 1998, 43 2573-2576; J. F. Dufour, et al. Ann Intern Me, 199,7 127, 981-98; Kaplan, R. A. et al. Ann Intern Med. 1997, 126, 682-688) and experimental animal models (G. Abdel-Aziz, 1990). An essential element of this recovery process is the apoptosis of activated HSC (J. P. Iredale et al J Clin Invest. 1998, 102 538-549). Understanding the mechanisms of HSC apoptosis might provide insight into novel therapeutic approaches to treat advanced hepatic fibrosis. HSC apoptosis are shown to be induced by activated Kupffer cells through a novel mechanism (Fischer R, et al. Gastroenterology. 2002; 123:845-61) and by ligands of the peripheral type benzodiazepine receptor (Fischer R, et al. Gastroenterology. 2001; 120:1212-1226). However, very little is known about the role of hepatocytes for HSC apoptosis. Murine hepatocytes have been shown to secreate an inducing protein that selectively causes apoptosis in liver (Ikeda et al, Immunology, 2003, 108,116-122). Hepatic stellate cells, when isolated and grown on plastic surface, spontaneously undergo activation. This culture induced activated stellate cells have been extensively studied as a model cell line of liver fibrogenesis.
The inventors have sought to address the issue of liver homeostasis and disease, particularly the interaction between hepatocytes and stellate cells. Is stellate cell growth controlled by immortalized hepatocytes? Do activated stellate cells in turn regulate hepatocyte growth? Understanding these interactions will offer new avenues for therapeutic strategies to combat liver disease.